package main

import (
	"encoding/json"
	"expvar"
	"fmt"
	"runtime"
	"time"
)

type Monitor struct {
	Alloc,
	TotalAlloc,
	Sys,
	Mallocs,
	Frees,
	LiveObjects,
	PauseTotalNs uint64

	NumGC        uint32
	NumGoroutine int
}

func NewMonitor(duration int) {
	var (
		m          = Monitor{}
		rtm        runtime.MemStats
		goroutines = expvar.NewInt("num_goroutine")
	)
	var interval = time.Duration(duration) * time.Second
	for {
		<-time.After(interval)

		// Read full mem stats
		runtime.ReadMemStats(&rtm)

		// Number of goroutines
		m.NumGoroutine = runtime.NumGoroutine()
		goroutines.Set(int64(m.NumGoroutine))

		// Misc memory stats
		m.Alloc = rtm.Alloc
		m.TotalAlloc = rtm.TotalAlloc
		m.Sys = rtm.Sys
		m.Mallocs = rtm.Mallocs
		m.Frees = rtm.Frees

		// Live objects = Mallocs - Frees
		m.LiveObjects = m.Mallocs - m.Frees

		// GC Stats
		m.PauseTotalNs = rtm.PauseTotalNs
		m.NumGC = rtm.NumGC

		// Just encode to json and print
		b, _ := json.Marshal(m)
		fmt.Println(string(b))
	}
}